The primary antigens of intact HIV virus exposed to the humoral immune system are the envelope glycoproteins. The mutation rate of the env gene, however, is very high and viral escape mutants emerge which evade the humoral immune response. In contrast to antibodies, class I restricted cytotoxic T cells (CTL) are often broadly cross-reactive because they are easily invoked by core proteins which readily target the class I restricted pathway of antigen recognition and have a lower rate of mutation. In this proposal we wish to examine the ability of the intracellular pathogen Listeria monocytogenes to deliver HIV proteins to the immune system. L. monocytogenes is a facultative intracellular bacterium which has the unique ability among organisms of this type to live and grow in the cytoplasm of cells. Thus antigens secreted by L. monocytogenes have direct access to the class I restricted pathway for antigen presentation to Cit. The immune response to L. monocytogenes antigens is thought to be restricted to a TH1, CD4+ T cell and CD8+ T cell response with only very weak TH2 T cell and humoral responses being engendered. An aspect of the immune response to HIV which has recently received a great deal of interest, is the role of the balance of humoral and cellular immunity as regulated by TH1 and TH2 CD4+ subsets in disease progression. Although still very controversial it has been suggested that the humoral immune response, far from being beneficial or even ineffective in HIV infection, may actually be harmful because it impairs the ability of the host to mount a protective cellular immune response. Thus L. monocytogenes may be the ideal vaccine vector for boosting the TH1, CD4+ and CD8+ T cell response to HIV proteins and a.unique system to prime the cellular immune response as a potential vaccine against HIV. In order to characterize the immune response to HIV proteins delivered by L. monocytogenes we have already stably expressed gag, pol and nef genes in L. monocytogenes in secretable form. We will use these recombinant organisms to generate HIV specific immune responses in the mouse which we will characterize in vivo and in vitro with respect to cell phenotype, MHC restriction and cytokine secretion. We will also examine the longevity of the immune response to HIV antigens delivered in this manner and the influence of routes of immunization and immunization protocols. In the second year of this proposal L. monocytogenes will be transformed to secrete the SIV equivalents of the antigens which appear in mice to invoke the strongest and most long lived cellular immune response for use in the simian model. Experiments in macaques will include virulence and pathology studies, persistence, and the ability of L. monocytogenes to invade and survive in bone-marrow macrophages. If the results of these experiments are encouraging, Dr. M. Murphey-Corb will perform protection experiments in the SIV: macaque model based on our most effective vaccine protocols at the Tulane Regional Primate Center.